How can I undo a Subversion (svn) merge without reverting?

Question

While trying to help a coworker figure out where some unit tests went bad in the svn history, I hastily reverse merged a commit that I thought might have been the problem into his working copy:

 svn merge -c -1234 .

then asked, "wait... you're working copy was clean right?". Unfortunately not. So a quick revert was not a good option. I tried to undo it cleanly ( svn merge -c 1234 ) but nothing happened. Luckily he knew exactly which files were changed so we made a patch, reverted all modified files, and applied the patch. However, I'm wondering if there was a cleaner way to get out of this situation.

Answer 1

Your original idea was almost right. The Subversion way to do this would have been

svn merge -c 1234 . --ignore-ancestry

to re-apply the reverse-merged commit.

Answer 2

I realized that the reason svn merge -c 1234 did not work was we were already beyond revision 1234, so svn saw no need to do anything. A solution I tried at my desk later, which worked, was to download a diff of commit 1234, then apply it as a patch. Note that I used 1234 and not -1234 , which would have been a reverse diff.

svn diff -c 1234 > undo.patch
svn patch undo.patch

Had I been in the original situation again, this would have undone the reverse merge cleanly while preserving my coworker's changes.